This page is based on a thesis of three students from the
St-Gertrudisinstitute
in Landen (B). Although I adapted and addedsome
things myself, the major research is done by them. Please mail me
before copying this. To see the printable version of these pages, click
here.

I) Introduction

Before 1905 there wasn't much to say about time. In the 17th century
Newton
defined time as something that continues, no matter what, without any
link
with reality and according to its own nature. Everybody believed that
time
had its influence on the environment, but if you believed that the
environment
had its influence on time, you really had to be mad! That changed in
1905
with Einstein's special relativity theory, in which he showed that time
can be influenced. But this doesn't mean time can be changed in such a
way that you can travel to the future or the past. That's what it's all
about on this pages: Is it possible to travel through time, and if
possible,
under which circumstances?
It will become very clear that the speed of light has got a major
influence
on the possibility of time travelling. An object should move faster
than
light speed to travel through time. Therefore we use the tunnel effect,
an effect in the quantum mechanics. That means that a ray of light or a
bundle of electrons that is sent through a certain barrier arrives
sooner
at the other side of the barrier than if there wasn't a barrier.
If time travelling is possible according to the relativity theory,
there
will be a lot of other problems. I'm not talking about the technical
problems,
'cause that's not what this is about, but I mean the paradoxes. For
these
problems there is no such thing as a logical explanation, no matter how
long you'll search.

II) Relativity

There are 2 sorts of physics: Newton's physics and Einstein's physics.
When you use formulas from Newton and formulas from Einstein's physics
to calculate a certain physical value, you'll become not the same
value.
In
'normal' situations these differences are extremely small. But in
'extreme'
situations these differences will become very big. For example: someone
who's in a train that moves with an incredible high speed (like 10 000
km/second) and who measures the distance between the sleepers of the
train,
will measure a smaller distance than someone who stands still beside
the
railway. According to the physics of Newton and our intuition we'd say
the distance would remain the same. In 'normal' situations that's
correct:
measuring in a train that moves at hundreds, thousands or even ten
thousands
kilometers/hour would make the difference in distance immeasurably
small.
Newton's laws would certainly do in these situations. But when the
speed
of the train approaches the speed of light, the difference will become
noticeable ('extreme' situations), and we would need Einstein's
physics.
According to the latest experiments, Einstein's formulas seem to be the
right ones.

Einstein's special theory of relativity was finished in 1905. It's
based
on the constant speed of light and the fact that speed isn't absolute;
when a helicopter lifts off you can also assume it's the chopper that
stands
still and the earth that moves. This theory describes the relation
between
observation of a certain phenomenon by observers that move with a
constant
speed related to each other.
The general theory of relativity was finished in 1912, but Einstein
couldn't
interpret his mathematical reasoning physically. He redeveloped the
theory,
not only based on mathematics but also on physics, and he ended up with
the same result as 3 years earlier. Then he published it. This theory
describes
on one hand the relation between the observations of the observers that
move with an accelerating speed related to each other. On the other
hand
it's about the influence of gravity on observations and the relation
between
observations that are done from places where gravity differs. Because a
constant speed can be looked at as a speed with acceleration 0, the
general
theory of gravity includes the special one.